Cartridge for more nearly uniform projectile velocities



Sept. 17, 1963 T. Q. CICCONE ETAL 3,103,884

CARTRIDGE FOR MORE NEARLY UNIFORM PROJECTILE VELOCITIES Filed March 1s,' 1962 INVENTORS. TH S Q. GICCONE J0 J- SCANLON BY .5}. mag 42. JEMJMQ ATTORNEY 3,103,884 CARTGE FGR MORE NEARLY UNIFORM PROIECTELE VELOQITIES Thomas Q. Cic'cone, Langhorne, Pa., and John J. Scanlon, Levittown, N.J., assignors to the United States of America as represented by the Secretary of the Army Filed Mar. 16, 1962, Ser. No. 180,372

3 Claims. (Cl. 102-45) (Granted under Title 35, U8. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon. p

This invention relates to an improved small arms cartridge, especially in sizes of .50 caliber and 20 millimeter,

and has for an object to provide a cartridge of this sort providing a more nearly uniform projectile velocity under wide temperature differences, as well as a cartridge providing a smaller variance in projectile velocities under substantially the same conditions.

Another object is to provide such a cartridge having greatly reduced if not totally eliminated danger of hangfire.

A further object is to provide a cartridge for an externally powered Gatling type gun such as are used in aircraft and elsewhere in which there is less danger from a cartridge exploding after it has been ejected from such a gun.

In propellants it has been known that a travelling wave of pressure is more critical than a traveling flame front because the former endangers the propellant grains to the likelihood of breaking into smaller sizes causing more rapid combustion and excessive pressure. Many suggestions have been made for solving this need but without much improvement. One such suggestion was for a core of black powder in the expectation the propellant would burn more nearly uniformly and radially outwardly. But this was not as good as had been expected.

Several years ago the explosives department of E. L du Pont de Nemours of Wilmington, Delaware, produced a core-type igniter that was much more rapid in burning than had been the black powder, and was known to the trade as pyrocore. It was made in numerous sizes and grades. A distinctive feature was a thin lead sheath around a high explosive and an oxidizer enclosed within the sheath. Some of these axial core lead sheath .igniters were no help at all in reducing the difference in projectile velocity under great temperature differences, but instead aggravated that variance in velocity due to temperature difference.

Under one view some of these lead sheath type axial igniters were investigated to ascertain which if any were best adapted for use in cartridges of about .50 caliber to 20 millimeter size to reduce the difference in combustion rate of propellant under wide temperature differences. It was found the ordinary or standard electric or percussion primer was unsuitable for igniting these pyrocore-type igniters because the primer energy was insufficient. A few grains of PETN (penta erythritol tetranitrate C H (ONO were used between the ignited and the usual electric or percussion primer but without success because the PETN was not always ignited at cold temperatures. Thinking a more sensitive booster to be necessary, 2 grains of lead azide, (Pbd N a primer material, was used with the PETN between the lead sheathed ignited and the primer. This proved satisfactory. It was next necessary to determine which of a number of kinds of these core igniters gave improved and the best results. This has now been done.

Referring to the drawing, FIG. 1 shows a longitudinal Patented Sept. 17, 1963 section through a preferred embodiment of a 20 millimeter cartridge.

FIG. 2 is a larger scale longitudinal section through the rear end of a booster found to be necessary between the primer and sheathed igniter of FIG. 1.

A standard 20 millimeter cartridge differs from that shown in FIG. 1 only in not having an axial lead sheathed type igniter embedded in the propellent and a booster found necessary between the primer and igniter." The cartridge illustrated includes the brass case 10, a projectile 11 of any usual sort, and some customary type of propellant 12. The projectile 11, as shown, contains a well known high explosive 13 such as: 52% aluminum powder, 35% ammonium perchlorate, 6% RDX/wax 97/3, 4% trinitrotoluene, 2% calcium stearate, 1% graphite and a rotating band 14. In the base of the cartridge is an electric primer 15. Unlike the standard cartridge, that of this invention includes an axial igniter having a lead sheath 16 and a booster 17 between the primer 15 and the igniter 16.

As shown in FIG. 2, the booster 17 includes 2 grains of PETN 18 with an equal weight of lead azide 19 between the primer 15 and the PETN portion 18 of the booster. Several different types of sheathed axial igniter 16a were tried. Each was not capable of being fired by the standard primer, either electric or percussion. Appreciating the need for a booster, a charge of PETN 'alone was first placed between the primer and igniter.

This was found to be inadequate so that an additional charge of a more sensitive material, namely lead azide, was used in order to obtain satisfactory ignition of the igniter and propellant. Either single or double base propellants were found to be satisfactorily operable.

The first notable change from using the sheathed axial igniter 16a was the discovery that due to the almost simultaneous ignition of the axial length of the propellant slightly less propellant of the same sort (about 2% less) was needed in the same brass case to obtain substantially the same average projectile velocities. The preferred sheathed axial igniter was found to be one containing about 2.0 grains per foot of PETN, 6.0 grains of aluminum barium peroxide (AlBaO per foot of igniter length, and 99.2 grains of lead sheath per foot of igniter. This had an outside diameter for the lead sheath of .073 inch with a flame front travel in the sheath of about 14,400 feet per second. The inside diameter of the sheath was about half that of its outside diameter. Between the time of circuit closing and rupture of a wire at the front of the gun was .065 millisecond with the aid of a Berkley counter, which is much more rapid than the time for the prior standard propellant without the sheathed axial igniter. The PETN and peroxide are each in the usual finely powdered form. The extreme rapidity of PETN burning plus the absorption of energy by the lead sheath which becomes probably vaporized by the heat of the explosion is what make the ignition of the propellant almost simultaneous along its axial length with a higher pressure being initially available for moving the projectile.

Other results are shown in the hereinafter table. There were ten rounds fired at each designated temperature and the average of the ten measured. The first three firing temperatures listed were of the standardized prior 20 millimeter cartridges without any sheathed igniter. Column 1 gives the conditioning temperatures under which the firings occurred. Column 2 shows the average velocity at 78 feet from the muzzle for each of the ten rounds in feet per second. Column 3 shows the difference in velocities at 78 feet at the indicated temperature extremes. This shows the first or standard cartridge which had no axial sheathed igniter. The primer composition for the standard electrically fired primer is:

40% lead styphnate, 14% calcium silicide, 44% barium nitrate, 1% acetylenic black, 1% gum arabic. The preferred embodiment of the axial sheathed igniter has been stated above.

While no igniter with less shattering effect was tested, these results convince us that a sheathed ignited for .30 caliber cartridges should have a lead sheath of about 73.0 to 99.4 grains per foot of length, with about 2 to 2.4 grains of PETN per foot of length, and about 5 to 5 .6 grains per foot of the aluminum barium peroxide. These tests show that the Weight of the lead sheath has substantial bearing on the brisance or shattering eflect and that a low shattering effect comparatively speaking is desirable. The reason is not known for a certainty but is believed to be because at +165 F. a substantial shattering effect may be more powerful than at 65 F. Possibly a relatively low shattering effect is desirable to reduce the danger of propellant being split into still smaller particles than are desired.

The prior standard cartridge without any axial sheathed igniter has an undesirable difference in projectile velocities of 208 feet per second between ignition at the high temperature of +165 F. and low of 65 F., while the preferred embodiment has only 107 feet per second and one of the larger sheathed igniters caused a greater difference in velocities between these temperatures than did the prior art.

The referred embodiment of sheathed igniter has been found desirable also for the .50 caliber cartridge but not tested in other sizes of cartridges.

Hangfire should be distinguished from a misfire. In the latter case the primer does not fire the propellant for some reason and the primer spark if developed does not ignite anything. A hangfire, on the other hand, is a situation where the primer has fired but the combustion somewhere is only smoldering or for some unknown cause is temporarily hanging but likely to go off. In artillery and small arms it has been required to wait some prescribed time before extracting the ammunition because of the danger of an explosion of a cartridge outside the gun injuring someone. In automatic guns dependent upon recoil to eject a cartridge the danger of hanglire is not so critical because the unfired cartridge is not i ejected automatically. In externally powered Gatling type guns such as are used in aircraft, there have already been injuries from hangfires. A hangfire is said to occur only one in every 250,000 or 300,000 shots. We have not been able to obtain that degree of test firings; however, the intensity of flame velocity within the lead sheath has convinced us that this type igniter is a cure for hanglires. A misfire in an externally powered Gatling type gun is no hazard but a hangfire is very dangerous.

The igniter of this invention is not only useful in re ducing the danger of hangfire but is also useful in obtaining more nearly uniform projectile velocity under widely different ambient temperatures.

We claim:

1. In a .50 caliber to 20 millimeter cartridge having a primer and propelling charge the combination therewith of the improvement for lowering the difference in muzzle velocity of a projectile fired by said cartridge at F. and at +165 F. said improvement including about 2 grains of lead azide (Pb N adjacent the primer, about 2 grains of PETN in front of the lead azide, and a propellant igniter extending longitudinally and axially of the cartridge and propellant, said igniter comprising a lead sheath having an outside diameter of about .073 inch and a weight of about 99.2 grains of lead per foot, and within said sheath about 2.0 grains of PETN per foot and about 6.0 grains of aluminum barium peroxide (AlBaO per foot, whereby the difference in muzzle velocity for a standard prior cartridge of a stated size under an ambient temperature of 65 F. and also under +165 F. has been reduced to about half the value of such a difference in velocities at those temperature-s without said improvement.

2. A cartridge of a size between about .30 caliber and 20 millimeter having a case, propellant therein, and a lead sheathed type igniter axially within the propellant and including about 2 to 2.4 grains of PETN per foot of the igniter, AlBaO in quantity from about 5 to 5.6 grains per foot, and about 73.0 to 99.4 grains per foot of lead sheath.

3. A 20 millimeter cartridge provided with means for reducing the danger of hangfire and for reducing the average velocity difference in temperatures of 65 F. and F. and therebetween, said means including a propellant coaxially enclosed Within a lead sheath containing an explosive and an oxidizer possessing an ignition rate in excess of 12,000 feet per second, said sheath enclosing an igniter fired by a primer, and a booster including about 2.4 grains of PETN per foot, about 5.6 grains of AlBaO per foot, and about 99.2 grains of lead in said sheath per foot.

References Cited in the file of this patent UNITED STATES PATENTS 2,926,566 Atkins et a1. Mar. 1, 1960 2,974,596 Allen Mar. 14, 1961 3,014,425 Turnbull et a1 Dec. 26, 1961 3,020,844- Miller Feb. 13, 1962 

1. IN A .50 CALIBER TO 20 MILLIMETER CARTRIDGE HAVING A PRIMER AND PROPELLING CARGE THE COMBINATION THEREWITH OF THE IMPROVEMENT FOR LOWERING THE DIFFERENCE IN MUZZLE VELOCITY OF A PROJECTILE FIRED BY SAID CARTRIDGE AT -65*F. AND AT +165*F. SAID IMPROVEMENT INCLUDING ABOUT 2 GRAINS OF LEAD AZIDE (PB2N6) ADJACENT THE PRIMER, ABOUT 2 GRAINS OF PETN IN FRONT OF THE LEAD AZIDE, AND A PROPELLANT IGNITER EXTENDING LONGITUDINALLY AND AXIALLY OF THE CARTRIDGE AND PROPELLANT, SAID IGNITER COMPRISING A LEAD SHEATH HAVING AN OUTSIDE DIAMETER OF ABOUT .073 INCH AND A WEIGHT OF ABOUT 99.2 GRAINS OF LEAD PER FOOT, AND WITHIN SAID SHEATH ABOUT 2.0 GRAINS OF PETN PER FOOT AND ABOUT 6.0 GRAINS OF ALUMINUM BARIUM PEROXIDE (ALBAO2) PER FOOT, WHEREBY THE DIFFERENC IN MUZZLE VELOCITY FOR A STANDARD PRIOR CARTRIDGE OF A STATED SIZE UNDER AN AMBIENT TEMPERATURE OF -65*F. AND ALSO 